Gasket-forming plastisols comprising vinyl chloride resin, fatty acid amides and salt of lauryl sulfate



Oct. 22, 1968 A. J. TESTA 3,406,854

GASKET'FORMING PLASTISOLS COMPRISING VINYL CHLORIDE RESIN, FATTY ACID AMIDES, AND

SALT OF LAURYL SULFATE Filed Dec. 22, 1965 INVENTOR. ANTHONY J. TESTA BY 7% MM ATTORNEY United States Patent GASKET-FORMING PLASTISOLS CQMPRISING VINYL CHLORIDE RESIN, FATTY ACID AM- IDES AND SALT 0F LAURYL SULFATE Anthony J. Testa, Westwood, Mass., assignor to W. R. Grace & Co., Cambridge, Mass., a corporation of Connecticut Filed Dec. 22, 1965, Ser. No. 515,632 9 Claims. (Cl. 215-40) ABSTRACT OF THE DISCLOSURE A gasket-forming composition for container closure elements composed of a plastisol of a vinyl chloride resin which includes a torque control additive consisting of a member selected from the group consisting of an alkali metal, alkaline earth metal and ammonium salt of lauryl sulfate combined with a mixture of unsaturated fatty acid amides.

This invention relates to compositions suitable for use as gaskets in rotatable closures. In a particular aspect, it rel-ates to a vinyl resin sealing composition which includes an additive to endow the resulting gasket with low removal torque values.

Rotatable closures are usually made of lacquered tinplate or aluminum and have gained extensive use in protecting and preserving foods in glass containers. To be effective, the closure requires a gasket to easily seal the contained food, and it must not include any deleterious substance that might transfer to and contaminate the food. Typical rotatable closures include the screw type and lug type, and they differ chiefly in the means by which the closure is held firmly in place on the container. Illustrative means include a continuous or discontinuous thread, projecting lugs, etc., located near the container opening, and they are adapted to mate in threaded engagement with the closure as it is rotatably advanced to bring the gasket into sealing relationship with the mouth of the container.

In sealing a jar with a closure, air is exhausted from the headspace above the contents in closing machines which produces a vacuum either mechanically or by the condensation of steam. In closing the container, the torque must be sutficient to resist retractive movement during shipment and/or storage as such movement is apt to break the seal and cause leaks through which spoilage organisms can gain access to the contents in the container.

The torque which is required for closure removals on vacuum-packed containers varies widely, but it is well known that some containers, such as baby food jars, have their caps so firmly attached that it is necessary to resort to fairly drastic means to effect their removal. On the other hand, closures may be so loosely attached that only a slight twist is required to remove it from the container. This is objectionable because the container is subject to tampering by customers who remove the closure when the container is stored on shelves in the market to examine the contents. It is apparent that such opening breaks the seal and exposes the contents to the atmosphere with the result that spoilage will gradual ly occur. Another objection is that a loosely-fitted closure may be accidently jarred, causing the seal to be broken and concomitantly therewith result in exposure of the contents to contamination.

It is, therefore, an object of this invention to provide a composition which is suitable for use as a gasket in a rotatable closure which maintains :a hermetic seal but has low removal torque requirements. This objective is achieved by incorporating into the composition an additive consisting of an admixture of (a) a member selected from the group consisting of alkali metal, alkaline earth metal and ammonium salts of lauryl sulfate, and (b) a mixture of fatty acid amides composed of a major amount of oleyl amide and minor amounts of stearyl amide and linoleyl amide. Illustrative salts of lauryl sulfate include sodium lauryl sulfate, potassium lauryl sulfate, magnesium lauryl sulfate and ammonium lauryl sulfate. An effective amide mixture consists of 91% oleyl amide, 6% stearyl amide, and 3% linoleyl amide. The additive consists of 1 to 8 parts of the salt of lauryl sulfate and 3 to 15 parts of the mixed amides. The preferred admixture consists of 2 to 4 parts of the salt and 6 to 10 parts of the amide mixture. All proportions are expressed on a Weight basis.

Closure manufacturers design their gaskets with the prime consideration of preventing accidental dislodgement of the closure. This requires formulation of the gasket-forming composition to be somewhat tacky so that it exhibits considerable friction to the closure and the container against rotational torque. But, this is precisely what makes these closures difiicult to open for the average consumer. By including the additive of this invention in the gasket, the frictional forces which exist between the gasket and the container are appreciably reduced without impairing the sealing efiiciency.

:Plastisols are frequently used to form gaskets for closures. These compositions basically comprise a vinyl resin dispersed in a plasticizer in which the resin is insoluble at room temperature but which is capable of solvating the resin at an elevated temperature The properties of these compositions may be modified by the addition of conventional ingredients, such as fillers, stabilizers, pigments and other additives.

The torque control additive which is included in the plastisol composition is largely incompatible with the resin and the plasticizer. It is possessed of limited compatibility, however, so that it remains within the body of the gasket when it is relaxed or uncompressed. As the gasket is subjected to pressure when the closure is brought into sealing relationship with a container, a portion of the additive migrates to the surface of the gasket and reduces the friction between the gasket and the lip of a container.

In the drawing:

FIG. 1 is a perspective sectional view showing the application of a gasket-forming composition by means of a nozzle in the peripheral channel of an inverted lugtype closure.

FIG. 2 is a fragmentary vertical sectional view of a closure in sealed relationship with a container.

The closure, shown generally at 10, comprises a circular panel 11 and a skirt 12 depending from the periphery of the panel. A gasket-receiving channel 13 is provided in the perimetrical margin of the panel adjacent the lower edge of the skirt. The upper edge of the skirt is curved inwardly to form a bead 14 into which are formed a series of spaced lugs 15. These lugs register with the thread 16 (shown in FIG. 2) formed on the neck of the container 17 and lock the closure in place.

The inner surface of the closure is usually coated with a protective film of a varnish or a lacquer, and the gaskets are generally formed from liquid compositions by a lining technique. In the lining operation, the closure is positioned over a rotating chuck (not shown) and the composition 18 flows through a nozzle 19 into the channel 13. The closure is spun by the chuck and the composition is distributed as a narrow band in the channel. The lined closures are then passed to a heated oven maint ained at a temperature sufficiently high to flux the composition which, when cooled, solidifies to a permanent rubber-like gasket 20 (as shown in FIG. 2). The fluxing step is generally carried out by continuously advancing the lined closures through an oven on a wire mesh belt, and the advance is so synchronized that a residence time in the oven of about 60 seconds is sufficient to flux the composition.

In applying a gasketed closure to a container, the gasket surface is initially dry to the touch, and as the closure is progressively advanced on the container, the increased pressure results in a corresponding increase in the exudation of additive to the surface. The greater the pressure the greater is the exudation, and migration of the additive continues until the closure is brought into sealing contact with the container. The resulting surface layer of additive, shown as an exaggerated film 21 in FIG. 2, remains on the gasket so long as the sealing relationship is maintained. The additive thus acts as a lubricant by reducing the frictional forces which exist between it and the container and, consequently, less torque is required to remove the closure. As the closure is progressively removed, the additive is gradually reabsorbed into the body of the gasket, and it is completely reabsorbed when the gasket is out of contact with the container.

Vinyl resin plastisols are particularly suitable for use in forming the gaskets. These include plasticized homopolymers of vinyl chloride and copolymers of vinyl chloride with up to 20% by weight of another monomer copolymerizable therewith. Suitable monomers include acrylonitrile, vinylidene chloride, vinyl acetate, and dialkyl maleates. Typical copolymers include 95 percent vinyl chloride-5% vinyl acetate; 95 percent vinyl chloride- 5% dialkyl maleate; and 94 percent vinyl chloride-6% vinylidene chloride. The preferred resin is plasticized pol-yvinyl chloride.

The plasticizers which may be used in the gasket-forming compositions include dialkyl phthalates, alkyl phthalyl alkyl glycolates, dialkyl esters of alkane dicarboxylic acids, acetyl trialkyl citrates, and trialkyl and triaryl phosphates. Particular plasticizers include dioctyl phthalate (di-Z-ethylhexyl phthalate), octyl decyl phthalate, ethyl pht halyl ethyl glycolate, butyl phthalyl butyl glycolate, diisobutyl adipate, dibutyl sebacate, acetyl dibutyl citrate, trioctyl phosphate and tricresyl phosphate. Other useful plasticizers include alkyl esters of fatty acids, such as octyl stearate; epoxidized triglycerides, such as epoxidized soybean oil; and polymeric polyester plasticizers, such as polymeric glycol adipate.

Various other additives may be included to modify the plastisol compositions. These include fillers, such as anhydrous calcium sulfate, talc, wood flour, diatomaceous earth and asbestos; stabilizers, such as tetrasodium pyro phosphate, tribasic lead silicate, calcium stearate, zinc stearate, dibasic lead stearate and organo-tin complexes; pigments, such as carbon black, titanium dioxide and aluminum powder; and dispersing agents such as zinc resinate, lecithin, glycol stearate, propylene glycol laurate and glycerol monooleate.

The proportions of the torque control additive are included in the gasket-forming composition in amounts sufficient to insure incompatibility in the plastisol system and will vary with the relative proportions and properties of the other components. In general, the amount of additive should range between about 6 and 16, preferably between about 6 and 12, parts by weight per hundred parts of resin. As a rule, no additive will be observed on the surface of the fluxed, uncompressed gasket, but it will appear when compression of the gasket exceeds 25 pounds per square inch. Unless an excessive amount of additive is used, the amount that will migrate with time is negligible, and the surface of the gasket will remain dry and tack-free.

Representative gasket-forming compositions which included the torque control additive of this invention were prepared for comparative purposes with other lubricating agents. The formulations were composed as follows:

*The mixed amides consisted of 91% oleyl amide, 6% stearyl amide and 3% linoleyl amide, by weight.

Each composition was deposited in the annular channel of a 63 mm. rotatable lug-type metal closure and fluxed in an oven at a temperature of 398 F. and a residence time of one minute.

Each closure containing the fluxed gasket was placed on -a 12 oz. glass jar containing a representative pack of cold fill, steam closed olives. The turndown torque to seal each container was 25 inch-lbs. which is customarily employed in commercial closure-applying machines. The closed containers were stored for two weeks at a temperature of 100 F., and the closures were then tested for ease of removal. The results of the tests are shown in Table II.

TABLE II Example No.: Removal torques (inch-lbs.) 1 41 2 95 3 28 It is noted that the inclusion of the torque control additive of this invention consisting of the admixture of sodium lauryl sulfate and the mixed amides provided relatively low removal torques compared with the use of either component alone. This synergistic effect is significant in that the frictional forces are reduced without adversely affecting the seal between the gasketed closure and the container.

I claim:

1. A torque control additive for gasket-forming compositions which consists of (a) 1 to 8 parts of a member selected from the group consisting of alkali metal, alkaline earth metal and ammonium salts of lauryl sulfate, and

(b) 5 to 15 parts of a mixture of fatty acid amides composed of a major amount of oleyl amide and minor amounts of stearyl amide and linoleyl amide, said proportions being expressed on a weight basis.

2. An additive according to claim 1 wherein the salt is sodium lauryl sulfate and the mixture of amides consists of 91 percent oleyl amide, 6 percent stearyl amide and 3 percent linoleyl amide, by weight.

3. A composition according to claim 2 which consists of 3 parts by weight of sodium lauryl sulfate and 8 parts by weight of the mixed amides.

4, A gasket-forming composition comprising a vinyl chloride resin, a plasticizer therefor and between about 6 and 16 parts by weight based on parts by weight of the resin of a torque control additive consisting of (a) 1 to 8 parts of a member selected from the group consisting of alkali metal, alkaline earth metal and ammonium salts of lauryl sulfate, and

(b) 5 to 15 parts of a mixture of fatty acid amides composed of a major amount of oleyl amide and minor amounts of stearyl amide and linoleyl amide, said proportions being expressed on a weight basis.

5. A composition according to claim 4 wherein the salt is sodium lauryl sulfate and the amide mixture consists of 91 percent oleyl amide, 6 percent stearyl amide and 3 percent linoleyl amide, by weight.

6. A composition according to claim 5 wherein the resin is polyvinyl chloride and the additive is composed of 3 parts by weight of sodium lauryl sulfate and 8 parts.

by Weight of the mixed amides based on 100 parts by weight of the resin.

7. A closure comprising a cap adapted to be rotatably attached to a container opening and a rubber-like gasket positioned in the cap to register in sealing relationship with the lip of the container, said gasket comprising a fluxed plastisol of a vinyl chloride resin containing between about 6 and 16 parts by weight based on 100 parts by weight of the resin of a torque control additive consisting of (a) 1 to 8 parts of a member selected from the group consisting of alkali metal, alkaline earth metal and ammonium salts of lauryl sulfate, and

(b) 5 to 15 parts of a mixture of fatty acid amides composed of a major amount of oleyl amide and minor amounts of stearyl amide and linoleyl amide, said proportions being expressed on a weight basis.

8. A closure according to claim 7 wherein the salt is DONALD E. CZAJA, Primary Examiner.

sodium lauryl sulfate and the mixture of amides consists of 91 percent oleyl amide, 6 percent stearyl amide and UNITED STATES PATENTS 2,874,863 2/1959 Unger et al. 215-40 3,061,130 10/1962 Husum 215-40 3,142,401 7/1964 Foss et a1. 215-40 3,231,529 1/1966 Kuhn et a1. 260-23 R. A. WHITE, Assistant Examiner. 

